Preparation of azo dyes.



I UNITED STATES Patented May 31, 1904;

WALTHER LOEB, or BONN, GERMANY, 'AssIeNoR TO 0. F. BOEHRINGER & SOEHNE, or MANNHEIM-WALDHOF, BADEN, GERMANY, A FIRM.

' PREPARATION OF AZO DYES;

SPECIFICATION forming part of Letters Patent No. 761,310, dated. May 31, 1904. Application filed March 16, 1903. Serial No. 147,973. (No specimens.)

To all whom it may concern:

Be it known thatI, WALTHER LOEB, a citizen'of' the German Empire, residing at Bonn, Germany, have invented certain new and useful Improvements in the Preparation of A Dyes; and I do hereby declare the following to be a full, clear, and exact description of the invention, such as will enable others skilled in the art to which it appertains to make and use the same.

As is known, azo bodies have hitherto been prepared by dissolving or suspending an amin in acid solution, diazotizing the same at a low temperature by means of' a nitrite, and mixing the. diazotized solution with the solution of what is known inthe art as a" coupling compound. Coupling is the property which certain bodies (among them the ami'ns and bodies on the other.

phenols) possess of combining with diazo.

compounds to form azo compounds. Coupling compounds are the compounds which take part in such combination-for example, amins or phenols on the one-hand and diazo I have succeeded in preparing azo dyes electrochemically in one process by combining diazotation' and coupling of the amin with a compound of. acid character in the same solution under the influence of the electriccur rent. The principle of, the operation depends upon the discharge of N02 anions in a nitrite bath atthe anode. When an amin is present, diazotation of said amin takes place. The

diazo compounds so formed are, however, Very unstable under these clrcumstances forthe reason that the oxidizing effect of the current, thesolution itself, and the resulting H higher temperature all combine to rapidly decompose diaZo bodies. I have found that by employing coupling compounds in connection with the above diazotizing reaction on an amin I canobtain a stable azo dye. Ifone of the first class of coupling compounds having an acid character is present when the above diazotation of the amin takes place, such coupling compound will combine at once with the diazo compound which is formed, producing thereby the corresponding azo compound 7 above.

The technical advantages of this new process compared with the purely chemical process are, first, that the three solutions formerly employed (solution of nitrite, solution of the amin solution of the coupling compound) are replaced by a single one; secondly, that cooling apparatus, as required by the old methods, may-be readily dispensed with, since the rise of temperature is only of advantage in my process. y

The method of carrying out my invention involves, preferably, though not necessarily, the separation of the bath-cell employed by a diaphragm into an anode and cathode chamber and pouring into the-former, the anode-chamber, an amin, the coupling compound, (preferably in the form of a soluble salt,) and nitrite, (preferably in the required molecular proportions,) all in aqueous solution or suspension. It is advantageous to start with a neutral solution, thefelectrolysis being then carried out without further addition to the bath. The reaction, generally speaking, is represented by the following equation:

RNH.+H.R".0H+HN0.:

- 'annncon rango As anode material platinum is the most suitable. The cathode may be of any metal. The conditions of current may be largely varied. The anode solution is kept well stirred during the operation.

In the following detail description I have illustrated my invention by examples which embody what I consider the preferable manner of carrying 'the same into effect.

. I. Preparation of the sodvlmn salt of mullinazo-Q-iuqa/athoZ-3. 6 wlsul fom'o actcZ, (Ponoerm Q For the anode-bath ten parts, by weight, of anilin, 32.7 parts, by weight, of R-acid, (fl-naphthol-disulfonic acid,) and 9.1 parts, by weight, potassium nitrite are mixed and stirred with one hundred parts of water, the'whole the process is interrupted, and from the deep:

red anode solution the dye (Ponceau 2G) is isolated by known methods. The reaction in this case proceeds according to the equation:

The current density may be varied from 0.5 to 7.5 amperes per square decimeter, the temperature from iO to centigrade. If the cell is divided by a diaphragm into an anode and a cathode chamber, the above two baths are of course placed into the respective chambers e. the first bath into the anode-chamber and the cathode-bath into the cathodechamber.

Further examples embodying my invention are given in the following tabular arrangement, it being understood that the anodebaths there given are treated as in the above example and that a dilute solution of potassium hydrate ispreferably used therewith as the cathode-'batl i Anode solution. i ggg Resulting dye.

II. 10 partsbenzidin. 60-EJO The dyestuff (Congo) 33 parts naphthiseparates in the onic acid. course of electroly- 9.3 parts potassisis.

um nitrite. parts water.

III. 10 parts diamisi- G0-90 The deep violet dye din. separates from the 13.6 parts sodium solution during the salt of [3- electrolysis. naphthol. 7 parts potassium nitrite. 100 parts water.

IV. 8 parts naph- 40 The dye may be sepath y 1 a m i n rated from the deepsulf. acid red solution by di- (1.4.) rect evaporation or 10.? parts R-aeid. by the addition of 3 parts KNO salt to the solution. 100 parts water.

V. 11 parts sodium 15-30 The coloring-matter saltoftoluymay be isolated lene diamin from the deeply-colsulf. acid. ored liquor, as in 11 parts R-acid. Ex. IV.

6.2 parts KN O 100 parts water.

VI. 11 parts sodium 15-30 From the red solution salt of sulfathe dye (tropaeolin nilic acid 000, No. 1) is ob- 8.5 parts a-naphtained by evaporathol sodium tion or by adding salt. salt to the solution.

4.4 parts KNO 100 parts water.

'leinperature.

Anode solution. degrees Q Resulting dye.

VII. 10 parts sodium 15-30 salt of 1.4- n a p 11 thylufrom thesolui ion by min-sulfonie addition of acids.

ac 6.8 parts sodium salt of B- naphthol. 3.6 parts KNO 100 parts water.

VIII. 9.2 partsbenzidnn 31.6 partsazo compound prepared from sulfanilic acid and resorein. (3.!) parts sodium nitrite. 100 parts water.

What I claim, and desire to secure by Letters Patent of the United States, is-

1. In the art of preparing azo compounds, the step which consists in submitting an amin to the anode action of the electric current.

2. In the art of preparing azo compounds, the process which consists in diazotizing the starting material by the anode action of an electric current and coupling the resultant diazo compound.

3. In the art ofpreparing azo compounds, the process which consists in subjecting an amin in nitrite-bath to the anode action of an electric current.

4:. In the art of preparing azo compounds, the process which consists in diazotizing the starting material by the anode action of an electric current and concurrently coupling the resultant diazo compound.

5. In the art of preparing azo compounds, the process which consists in submitting an amin in a nitrite-bath to the anode action of an electric current and concurrently reacting thereon with a coupling compound.

6. In the art of preparing azo compounds, the process which consists in submitting an amin in a nitrite-bath to the anode action of an electric current in the presence of a coupling compound.

7. In the art of preparing azo compounds, the process which consists in submitting an amin in a nitrite-bath to the anode action of an electric current and concurrently reacting thereon with an acid coupling compound.

8. In the art of preparing azo compounds, the process which consists in submitting an amin in a nitrite-bath to the anode action of an electric current in the presence of an acid coupling compound.

9. The process of preparing azo dyes which consists in subjecting a mixture of amin, nitrite and acid coupling compound in an aqueous bath to the anode influence of the electric current.

10. The process of preparing azo dyes which consists in subjecting a mixture of amin, nitrite and acid coupling compound, in the required molecular proportions, in an aqueous bath to the anode action ofan electric current.

11. The process of preparing azo dyes which consists in subjecting a mixtureof amin, nitrite and salt of an acid coupling compound, in the required molecular proportions, in an aqueous bath to the action of an electric current.

p 12. The process of preparing azo dyes which consists in subjecting a mixture of amin, nitrite and acid coupling compound, in the required molecular proportions, in an aqueous bath to the anode action of an electric cur rent, and separating the dye thus formed from the bath by suitable methods. 7

13. The process of preparing the azo dye Ponceau 2G by subjecting a mixture of the following ingredients in the weight proportions substantially as stated: anilin, ten parts,

fi-naphthol-disulfonic acid, 32.7 parts, potassium nitrite, 9.1 parts and water one hundred parts, to the" anode action of an electric current.

14. The process of preparing the azo dye Ponceau 2G by subjecting a mixture of the following ingredients in the weight proportions substantially as stated: anilin, ten parts, fl-naphthol-disulfonic acid, 32.7 parts, potassium nitrite, 9.1 parts and water one hundred parts, tothe anode action of an electric'current in the presence of a platinum cathode.

In testimony whereof I affix my signature in presence of two witnesses.

WALTHER LOEB.

Witnesses:

W. FRI-IRE. VON LYNcKER, CARL ScHMI'rT. 

